1. Field of the Invention
The present invention relates to styrene-based polymer moldings and a process for production thereof. More particularly, it relates to moldings of styrene-based polymers having mainly syndiotactic configuration and also a high crystallinity (high degree of crystallization), which are excellent in heat resistance and chemical resistance, and a process for production thereof.
2. Description of the Related Art
Styrene-based polymers conventionally produced by radical polymerization, for example, have atactic configuration and are molded into various forms by various molding methods, such as injection molding, extrusion molding, blow molding, vacuum molding and casting, and are widely used in home electric appliances, office apparatuses, household articles, wrapping containers, toys, furniture, synthetic articles and other industrial materials.
These atactic styrene-based polymers, however, do not crystallize and thus have a disadvantage of being poor in heat resistance and chemical resistance.
The present inventors' group has succeeded in developing styrene-based polymers having a high syndiotacticity (Japanese Patent Application Laid-Open No. 104818/1987). These styrene-based polymers having syndiotactic configuration are crystalline polymers and are superior to styrene-based polymers having atactic configuration in mechanical strength, heat resistance and so on. However, moldings made of such syndiotactic styrene-based polymers do not have uniform crystallinity nor satisfactory physical properties such as quality stability and heat resistance.
Extensive investigations were carried out to produce moldings with excellent physical properties from the aforementioned syndiotactic styrene-based polymers. As a result, it was found that applying heat treatment to moldings of non-crystalline styrene-based polymers having syndiotactic configuration is effective for this purpose (Japanese Patent Application Laid-Open No.98431/1988). However, in order to obtain moldings with desired physical properties resulting from applying heat treatment, there still remained problems to be solved, for example, the need of lengthening the heat treatment time, and the need of maintaining dimensional stability at high level during heat treatment.